Group III nitride based quantum well light emitting device structures with an indium containing capping structure

ABSTRACT

Group III nitride based light emitting devices and methods of fabricating Group III nitride based light emitting devices are provided. The emitting devices include an n-type Group III nitride layer, a Group III nitride based active region on the n-type Group III nitride layer and comprising at least one quantum well structure, a Group III nitride layer including indium on the active region, a p-type Group III nitride layer including aluminum on the Group III nitride layer including indium, a first contact on the n-type Group III nitride layer and a second contact on the p-type Group III nitride layer. The Group III nitride layer including indium may also include aluminum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/698,658, filed Feb. 2, 2010 now U.S. Pat. No. 8,044,384, entitledGROUP III NITRIDE BASED QUANTUM WELL LIGHT EMITTING DEVICE STRUCTURESWITH AN INDIUM CONTAINING CAPPING STRUCTURE. U.S. patent applicationSer. No. 12/698,658 is a continuation of U.S. patent application Ser.No. 10/899,791 filed Jul. 27, 2004 now U.S. Pat. No. 7,692,182 entitledGROUP III NITRIDE BASED QUANTUM WELL LIGHT EMITTING DEVICE STRUCTURESWITH AN INDIUM CONTAINING CAPPING STRUCTURE, which is acontinuation-in-part of U.S. patent application Ser. No. 10/140,796filed May 7, 2002 now U.S. Pat. No. 6,958,497 entitled GROUP III NITRIDEBASED LIGHT EMITTING DIODE STRUCTURES WITH A QUANTUM WELL ANDSUPERLATTICE, GROUP III NITRIDE BASED QUANTUM WELL STRUCTURES AND GROUPIII NITRIDE BASED SUPERLATTICE STRUCTURES which claims the benefit of,and priority from, Provisional Application Ser. No. 60/294,445, filedMay 30, 2001 entitled MULTI-QUANTUM WELL LIGHT EMITTING DIODE STRUCTURE,Provisional Application Ser. No. 60/294,308, filed May 30, 2001 entitledLIGHT EMITTING DIODE STRUCTURE WITH SUPERLATTICE STRUCTURE andProvisional Application Ser. No. 60/294,378, filed May 30, 2001 entitledLIGHT EMITTING DIODE STRUCTURE WITH MULTI-QUANTUM WELL AND SUPERLATTICESTRUCTURE. U.S. patent application Ser. No. 12/698,658 is also acontinuation-in-part of U.S. patent application Ser. No. 11/875,353,filed Oct. 19, 2007 now U.S. Pat. No. 8,227,268, which is a divisionalof U.S. patent application Ser. No. 10/963,666, filed Oct. 13, 2004 nowU.S. Pat. No. 7,312,474, which is a divisional of U.S. patentapplication Ser. No. 10/140,796 filed May 7, 2002 now U.S. Pat. No.6,958,497, which claims the benefit of, and priority from, ProvisionalApplication Ser. No. 60/294,445, filed May 30, 2001, ProvisionalApplication Ser. No. 60/294,308, filed May 30, 2001, and ProvisionalApplication Ser. No. 60/294,378, filed May 30, 2001. The disclosures ofall of the above-referenced applications are hereby incorporated hereinby reference in their entireties as if set forth fully herein.

FIELD OF THE INVENTION

This invention relates to microelectronic devices and fabricationmethods therefor, and more particularly to structures which may beutilized in Group III nitride semiconductor devices, such as lightemitting diodes (LEDs).

BACKGROUND OF THE INVENTION

Light emitting diodes are widely used in consumer and commercialapplications. As is well known to those having skill in the art, a lightemitting diode generally includes a diode region on a microelectronicsubstrate. The microelectronic substrate may comprise, for example,gallium arsenide, gallium phosphide, alloys thereof, silicon carbideand/or sapphire. Continued developments in LEDs have resulted in highlyefficient and mechanically robust light sources that can cover thevisible spectrum and beyond. These attributes, coupled with thepotentially long service life of solid state devices, may enable avariety of new display applications, and may place LEDs in a position tocompete with the well entrenched incandescent lamp.

One difficulty in fabricating Group III nitride based LEDs, such asgallium nitride based LEDs, has been with the fabrication of highquality gallium nitride. Typically, gallium nitride LEDs have beenfabricated on sapphire or silicon carbide substrates. Such substratesmay result in mismatches between the crystal lattice of the substrateand the gallium nitride. Various techniques have been employed toovercome potential problems with the growth of gallium nitride onsapphire and/or silicon carbide. For example, aluminum nitride (AlN) maybe utilized as a buffer between a silicon carbide substrate and a GroupIII active layer, particularly a gallium nitride active layer.Typically, however, aluminum nitride is insulating rather thanconductive. Thus, structures with aluminum nitride buffer layerstypically require shorting contacts that bypass the aluminum nitridebuffer to electrically link the conductive silicon carbide substrate tothe Group III nitride active layer.

Alternatively, conductive buffer layer materials such as gallium nitride(GaN), aluminum gallium nitride (AlGaN), or combinations of galliumnitride and aluminum gallium nitride may allow for elimination of theshorting contacts typically utilized with AlN buffer layers. Typically,eliminating the shorting contact reduces the epitaxial layer thickness,decreases the number of fabrication steps required to produce devices,reduces the overall chip size, and/or increases the device efficiency.Accordingly, Group III nitride devices may be produced at lower costwith a higher performance. Nevertheless, although these conductivebuffer materials offer these advantages, their crystal lattice matchwith silicon carbide is less satisfactory than is that of aluminumnitride.

The above described difficulties in providing high quality galliumnitride may result in reduced efficiency the device. Attempts to improvethe output of Group III nitride based devices have included differingconfigurations of the active regions of the devices. Such attempts have,for example, included the use of single and/or double heterostructureactive regions. Similarly, quantum well devices with one or more GroupIII nitride quantum wells have also been described. While such attemptshave improved the efficiency of Group III based devices, furtherimprovements may still be achieved.

SUMMARY OF THE INVENTION

Some embodiments of the present invention provide Group III nitridebased light emitting devices and methods of fabricating Group IIInitride based light emitting devices that include an n-type Group IIInitride layer, a Group III nitride based active region on the n-typeGroup III nitride layer and including at least one quantum wellstructure, a Group III nitride layer including indium on the activeregion, a p-type Group III nitride layer including aluminum on the GroupIII nitride layer including indium, a first contact on the n-type GroupIII nitride layer and a second contact on the p-type Group III nitridelayer.

In further embodiments of the present invention, the Group III nitridelayer including indium also includes aluminum. For example, the GroupIII nitride layer including indium may include InAlGaN. The Group IIInitride layer including indium may also include InGaN. The Group IIInitride layer including indium may be from about 20 to about 320 Åthick.

In particular embodiments of the present invention, the Group IIInitride layer including indium includes a layer of InAlGaN having ahigher Al composition in a region distal from the active region than ispresent in a region proximate the active region. In some embodiments,the InAlGaN layer may be continuously graded. In other embodiments, theInAlGaN layer may include a plurality of InAlGaN layers having differentAl and/or In compositions.

In further embodiments of the present invention, the Group III nitridelayer including indium includes a first layer ofIn_(x)Al_(y)Ga_(1-x-y)N, where 0<x≦0.2 and 0≦y≦0.4 and a second layer ofIn_(w)Al_(z)Ga_(1-w-z)N, where 0<w≦0.2 and y≦z<1. The first layer mayhave a thickness of from about 10 to about 200 Å and the second layermay have a thickness of from about 10 to about 120 Å. In particularembodiments, the first layer has a thickness of about 80 Å, x=0.1 andy=0.25 and the second layer has a thickness of about 30 Å, w=0.05 andz=0.55.

In additional embodiments of the present invention, the light emittingdevices further include a p-type Group III nitride layer disposedbetween the second contact and the p-type Group III nitride layerincluding aluminum. The p-type Group III nitride layer disposed betweenthe second contact and the p-type Group III nitride layer includingaluminum may also include indium. The p-type Group III nitride layerincluding aluminum may also include indium.

In certain embodiments of the present invention, the light emittingdevices include a silicon carbide substrate disposed between the firstcontact and the n-type Group III nitride layer.

Some embodiments of the present invention provide light emitting devicesand methods of fabricating light emitting devices that include an n-typegallium nitride based layer on a substrate, a gallium nitride basedactive region on the n-type gallium nitride based layer and include atleast one quantum well structure, a gallium nitride based layerincluding indium on the active region, a p-type gallium nitride basedlayer including aluminum on the gallium nitride based layer includingindium, a first contact on the n-type gallium nitride based layer and asecond contact on the p-type gallium nitride based layer.

In particular embodiments of the present invention, the n-type galliumnitride layer includes an n-type AlGaN layer on the substrate and ann-type GaN layer on the n-type AlGaN layer. The gallium nitride basedactive region may include a plurality of InGaN/GaN quantum wells.

In further embodiments of the present invention, the p-type galliumnitride based layer includes a p-type AlGaN layer on the gallium nitridebased layer including indium and a p-type GaN layer on the p-type AlGaNlayer. The second contact is on the p-type GaN layer. The galliumnitride based layer including indium may include a first layer ofIn_(x)Al_(y)Ga_(1-x-y)N, where 0<x≦0.2 and 0≦y≦0.4 and a second layer ofIn_(w)Al_(z)Ga_(1-w-z)N, where 0<w≦0.2 and y≦z<1. The first layer mayhave a thickness of from about 10 to about 200 Å and the second layermay have a thickness of from about 10 to about 120 Å. In particularembodiments of the present invention, the first layer has a thickness ofabout 80 Å, x=0.1 and y=0.25 and the second layer has a thickness ofabout 30 Å, w=0.05 and z=0.55.

In still further embodiments of the present invention, the substrate isa silicon carbide substrate and the first contact is on the siliconcarbide substrate opposite the n-type AlGaN layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features of the present invention will be more readily understoodfrom the following detailed description of specific embodiments thereofwhen read in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a Group III nitride light emittingdiode incorporating embodiments of the present invention;

FIG. 2 is a schematic illustration of a Group III nitride light emittingdiode incorporating further embodiments of the present invention;

FIG. 3 is a schematic illustration of a quantum well structure and amulti-quantum well structure according to additional embodiments of thepresent invention; and

FIG. 4 is a schematic illustration of a Group III nitride light emittingdiode incorporating further embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. However, this invention should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. In the drawings, the thickness of layers and regions areexaggerated for clarity. Like numbers refer to like elements throughout.As used herein the term “and/or” includes any and all combinations ofone or more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present. Itwill also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Like numbers refer to like elementsthroughout the specification.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present invention.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in the Figures is turned over, elements describedas being on the “lower” side of other elements would then be oriented on“upper” sides of the other elements. The exemplary term “lower”, cantherefore, encompasses both an orientation of “lower” and “upper,”depending of the particular orientation of the figure. Similarly, if thedevice in one of the figures is turned over, elements described as“below” or “beneath” other elements would then be oriented “above” theother elements. The exemplary terms “below” or “beneath” can, therefore,encompass both an orientation of above and below.

Embodiments of the present invention are described herein with referenceto cross-section illustrations that are schematic illustrations ofidealized embodiments of the present invention. As such, variations fromthe shapes of the illustrations as a result, for example, ofmanufacturing techniques and/or tolerances, are to be expected. Thus,embodiments of the present invention should not be construed as limitedto the particular shapes of regions illustrated herein but are toinclude deviations in shapes that result, for example, frommanufacturing. For example, an etched region illustrated or described asa rectangle will, typically, have rounded or curved features. Thus, theregions illustrated in the figures are schematic in nature and theirshapes are not intended to illustrate the precise shape of a region of adevice and are not intended to limit the scope of the present invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

It will also be appreciated by those of skill in the art that referencesto a structure or feature that is disposed “adjacent” another featuremay have portions that overlap or underlie the adjacent feature.

Although various embodiments of LEDs disclosed herein include asubstrate, it will be understood by those skilled in the art that thecrystalline epitaxial growth substrate on which the epitaxial layerscomprising an LED are grown may be removed, and the freestandingepitaxial layers may be mounted on a substitute carrier substrate orsubmount which may have better thermal, electrical, structural and/oroptical characteristics than the original substrate. The inventiondescribed herein is not limited to structures having crystallineepitaxial growth substrates and may be utilized in connection withstructures in which the epitaxial layers have been removed from theiroriginal growth substrates and bonded to substitute carrier substrates.

Embodiments of the present invention will be described with reference toFIG. 1 that illustrates a light emitting diode (LED) structure 40. TheLED structure 40 of FIG. 1 includes a substrate 10, which is preferably4H or 6H n-type silicon carbide. Substrate 10 may also comprisesapphire, bulk gallium nitride or another suitable substrate. Alsoincluded in the LED structure 40 of FIG. 1 is a layered semiconductorstructure comprising gallium nitride-based semiconductor layers onsubstrate 10. Namely, the LED structure 40 illustrated includes thefollowing layers: a conductive buffer layer 11, a first silicon-dopedGaN layer 12, a second silicon doped GaN layer 14, a superlatticestructure 16 comprising alternating layers of silicon-doped GaN and/orInGaN, an active region 18, which may be provided by a multi-quantumwell structure, an undoped GaN and/or AlGaN layer 22, an AlGaN layer 30doped with a p-type impurity, and a GaN contact layer 32, also dopedwith a p-type impurity. The structure further includes an n-type ohmiccontact 23 on the substrate 10 and a p-type ohmic contact 24 on thecontact layer 32.

Buffer layer 11 is preferably n-type AlGaN. Examples of buffer layersbetween silicon carbide and group III-nitride materials are provided inU.S. Pat. Nos. 5,393,993 and 5,523,589, and U.S. application Ser. No.09/154,363 entitled “Vertical Geometry InGaN Light Emitting Diode”assigned to the assignee of the present invention, the disclosures ofwhich are incorporated by reference as if fully set forth herein.Similarly, embodiments of the present invention may also includestructures such as those described in U.S. Pat. No. 6,201,262 entitled“Group III Nitride Photonic Devices on Silicon Carbide Substrates WithConductive Buffer Interlay Structure,” the disclosure of which isincorporated herein by reference as if set forth fully herein.

GaN layer 12 is preferably between about 500 and 4000 nm thick inclusiveand is most preferably about 1500 nm thick. GaN layer 12 may be dopedwith silicon at a level of about 5×10¹⁷ to 5×10¹⁸ cm⁻³. GaN layer 14 ispreferably between about 10 and 500 Å thick inclusive, and is mostpreferably about 80 Å thick. GaN layer 14 may be doped with silicon at alevel of less than about 5×10¹⁹ cm⁻³.

As illustrated in FIG. 1, a superlattice structure 16 according toembodiments of the present invention includes alternating layers ofIn_(X)Ga_(1-X)N and In_(Y)Ga_(1-Y)N, wherein X is between 0 and 1inclusive and X is not equal to Y. Preferably, X=0 and the thickness ofeach of the alternating layers of InGaN is about 5-40 Å thick inclusive,and the thickness of each of the alternating layers of GaN is about5-100 Å thick inclusive. In certain embodiments, the GaN layers areabout 30 Å thick and the InGaN layers are about 15 Å thick. Thesuperlattice structure 16 may include from about 5 to about 50 periods(where one period equals one repetition each of the In_(X)Ga_(1-X)N andIn_(Y)Ga_(1-Y)N layers that comprise the superlattice). In oneembodiment, the superlattice structure 16 comprises 25 periods. Inanother embodiment, the superlattice structure 16 comprises 10 periods.The number of periods, however, may be decreased by, for example,increasing the thickness of the respective layers. Thus, for example,doubling the thickness of the layers may be utilized with half thenumber of periods. Alternatively, the number and thickness of theperiods may be independent of one another.

Preferably, the superlattice 16 is doped with an n-type impurity such assilicon at a level of from about 1×10¹⁷ cm⁻³ to about 5×10¹⁹ cm³. Such adoping level may be actual doping or average doping of the layers of thesuperlattice 16. If such doping level is an average doping level, thenit may be beneficial to provide doped layers adjacent the superlatticestructure 16 that provide the desired average doping which the doping ofthe adjacent layers is averaged over the adjacent layers and thesuperlattice structure 16. By providing the superlattice 16 betweensubstrate 10 and active region 18, a better surface may be provided onwhich to grow InGaN-based active region 18. While not wishing to bebound by any theory of operation, the inventors believe that straineffects in the superlattice structure 16 provide a growth surface thatis conducive to the growth of a high-quality InGaN-containing activeregion. Further, the superlattice is known to influence the operatingvoltage of the device. Appropriate choice of superlattice thickness andcomposition parameters can reduce operating voltage and increase opticalefficiency.

The superlattice structure 16 may be grown in an atmosphere of nitrogenor other gas, which enables growth of higher-quality InGaN layers in thestructure. By growing a silicon-doped InGaN/GaN superlattice on asilicon-doped GaN layer in a nitrogen atmosphere, a structure havingimproved crystallinity and conductivity with optimized strain may berealized.

In certain embodiments of the present invention, the active region 18may comprise a single or multi-quantum well structure as well as singleor double heterojunction active regions. In particular embodiments ofthe present invention, the active region 18 comprises a multi-quantumwell structure that includes multiple InGaN quantum well layersseparated by barrier layers (not shown in FIG. 1).

Layer 22 is provided on active region 18 and is preferably undoped GaNor AlGaN between about 0 and 120 Å thick inclusive. As used herein,undoped refers to a not intentionally doped. Layer 22 is preferablyabout 35 Å thick. If layer 22 comprises AlGaN, the aluminum percentagein such layer is preferably about 10-30% and most preferably about 24%.The level of aluminum in layer 22 may also be graded in a stepwise orcontinuously decreasing fashion. Layer 22 may be grown at a highertemperature than the growth temperatures in quantum well region 25 inorder to improve the crystal quality of layer 22. Additional layers ofundoped GaN or AlGaN may be included in the vicinity of layer 22. Forexample, LED 1 may include an additional layer of undoped AlGaN about6-9 Å thick between the active region 18 and the layer 22.

An AlGaN layer 30 doped with a p-type impurity such as magnesium isprovided on layer 22. The AlGaN layer 30 may be between about 0 and 300Å thick inclusive and is preferably about 130 Å thick. A contact layer32 of p-type GaN is provided on the layer 30 and is preferably about1800 Å thick. Ohmic contacts 24 and 25 are provided on the p-GaN contactlayer 32 and the substrate 10, respectively.

FIG. 2 illustrates further embodiments of the present inventionincorporating a multi-quantum well active region. The embodiments of thepresent invention illustrated in FIG. 2 include a layered semiconductorstructure 100 comprising gallium nitride-based semiconductor layersgrown on a substrate 10. As described above, the substrate 10 may beSiC, sapphire or bulk gallium nitride. As is illustrated in FIG. 2, LEDsaccording to particular embodiments of the present invention may includea conductive buffer layer 11, a first silicon-doped GaN layer 12, asecond silicon doped GaN layer 14, a superlattice structure 16comprising alternating layers of silicon-doped GaN and/or InGaN, anactive region 125 comprising a multi-quantum well structure, an undopedGaN or AlGaN layer 22, an AlGaN layer 30 doped with a p-type impurity,and a GaN contact layer 32, also doped with a p-type impurity. The LEDsmay further include an n-type ohmic contact 23 on the substrate 10 and ap-type ohmic contact 24 on the contact layer 32. In embodiments of thepresent invention where the substrate 10 is sapphire, the n-type ohmiccontact 23 would be provided on n-type GaN layer 12 and/or n-type GaNlayer 14.

As described above with reference to FIG. 1, buffer layer 11 ispreferably n-type AlGaN. Similarly, GaN layer 12 is preferably betweenabout 500 and 4000 nm thick inclusive and is most preferably about 1500nm thick. GaN layer 12 may be doped with silicon at a level of about5×10¹⁷ to 5×10¹⁸ cm⁻³. GaN layer 14 is preferably between about 10 and500 Å thick inclusive, and is most preferably about 80 Å thick. GaNlayer 14 may be doped with silicon at a level of less than about 5×10¹⁹cm⁻³. The superlattice structure 16 may also be provided as describedabove with reference to FIG. 1.

The active region 125 comprises a multi-quantum well structure thatincludes multiple InGaN quantum well layers 120 separated by barrierlayers 118. The barrier layers 118 comprise In_(X)Ga_(1-X)N where 0≦X<1.Preferably the indium composition of the barrier layers 118 is less thanthat of the quantum well layers 120, so that the barrier layers 118 havea higher bandgap than quantum well layers 120. The barrier layers 118and quantum well layers 120 may be undoped (i.e. not intentionally dopedwith an impurity atom such as silicon or magnesium). However, it may bedesirable to dope the barrier layers 118 with Si at a level of less than5×10¹⁹ cm⁻³, particularly if ultraviolet emission is desired.

In further embodiments of the present invention, the barrier layers 118comprise Al_(X)In_(Y)Ga_(1-X-Y)N where 0<X<1, 0≦Y<1 and X+Y≦1. Byincluding aluminum in the crystal of the barrier layers 118, the barrierlayers 118 may be lattice-matched to the quantum well layers 120,thereby providing improved crystalline quality in the quantum welllayers 120, which increases the luminescent efficiency of the device.

Referring to FIG. 3, embodiments of the present invention that provide amulti-quantum well structure of a gallium nitride based device areillustrated. The multi-quantum well structure illustrated in FIG. 3 mayprovide the active region of the LEDs illustrated in FIG. 1 and/or FIG.2. As seen in FIG. 3, an active region 225 comprises a periodicallyrepeating structure 221 comprising a well support layer 218 a havinghigh crystal quality, a quantum well layer 220 and a cap layer 218 bthat serves as a protective cap layer for the quantum well layer 220.When the structure 221 is grown, the cap layer 218 b and the wellsupport layer 218 a together form the barrier layer between adjacentquantum wells 220. Preferably, the high quality well support layer 218 ais grown at a higher temperature than that used to grow the InGaNquantum well layer 220. In some embodiments of the present invention,the well support layer 218 a is grown at a slower growth rate than thecap layer 218 b. In other embodiments, lower growth rates may be usedduring the lower temperature growth process and higher growth ratesutilized during the higher temperature growth process. For example, inorder to achieve a high quality surface for growing the InGaN quantumwell layer 220, the well support layer 218 a may be grown at a growthtemperature of between about 700 and 900° C. Then, the temperature ofthe growth chamber is lowered by from about 0 to about 200° C. to permitgrowth of the high-quality InGaN quantum well layer 220. Then, while thetemperature is kept at the lower InGaN growth temperature, the cap layer218 b is grown. In that manner, a multi-quantum well region comprisinghigh quality InGaN layers may be fabricated.

The active regions 125 and 225 of FIGS. 2 and 3 are preferably grown ina nitrogen atmosphere, which may provide increased InGaN crystalquality. The barrier layers 118, the well support layers 218 a and/orthe cap layers 218 b may be between about 50-400 Å thick inclusive. Thecombined thickness of corresponding ones of the well support layers 218a and the cap layers 218 b may be from about 50-400 Å thick inclusive.Preferably, the barrier layers 118 the well support layers 218 a and/orthe cap layers 218 b are greater than about 90 Å thick and mostpreferably are about 225 Å thick. Also, it is preferred that the wellsupport layers 218 a be thicker than the cap layers 218 b. Thus, the caplayers 218 b are preferably as thin as possible while still reducing thedesorption of Indium from or the degradation of the quantum well layers220. The quantum well layers 120 and 220 may be between about 10-50 Åthick inclusive. Preferably, the quantum well layers 120 and 220 aregreater than 20 Å thick and most preferably are about 25 Å thick. Thethickness and percentage of indium in the quantum well layers 120 and220 may be varied to produce light having a desired wavelength.Typically, the percentage of indium in quantum well layers 120 and 220is about 25-30%, however, depending on the desired wavelength, thepercentage of indium has been varied from about 5% to about 50%.

In preferred embodiments of the present invention, the bandgap of thesuperlattice structure 16 exceeds the bandgap of the quantum well layers120. This may be achieved by adjusting the average percentage of indiumin the superlattice 16. The thickness (or period) of the superlatticelayers and the average Indium percentage of the layers should be chosensuch that the bandgap of the superlattice structure 16 is greater thanthe bandgap of the quantum wells 120. By keeping the bandgap of thesuperlattice 16 higher than the bandgap of the quantum wells 120,unwanted absorption in the device may be minimized and luminescentemission may be maximized. The bandgap of the superlattice structure 16may be from about 2.95 eV to about 3.35 eV. In a preferred embodiment,the bandgap of the superlattice structure 16 is about 3.15 eV.

In additional embodiments of the present invention, the LED structureillustrated in FIG. 2 includes a spacer layer 17 disposed between thesuperlattice 16 and the active region 125. The spacer layer 17preferably comprises undoped GaN. The presence of the optional spacerlayer 17 between the doped superlattice 16 and active region 125 maydeter silicon impurities from becoming incorporated into the activeregion 125. This, in turn, may improve the material quality of theactive region 125 that provides more consistent device performance andbetter uniformity. Similarly, a spacer layer may also be provided in theLED structure illustrated in FIG. 1 between the superlattice 16 and theactive region 18.

Returning to FIG. 2, the layer 22 may be provided on the active region125 and is preferably undoped GaN or AlGaN between about 0 and 120 Åthick inclusive. The layer 22 is preferably about 35 Å thick. If thelayer 22 comprises AlGaN, the aluminum percentage in such layer ispreferably about 10-30% and most preferably about 24%. The level ofaluminum in the layer 22 may also be graded in a stepwise orcontinuously decreasing fashion. The layer 22 may be grown at a highertemperature than the growth temperatures in the active region 125 inorder to improve the crystal quality of the layer 22. Additional layersof undoped GaN or AlGaN may be included in the vicinity of layer 22. Forexample, the LED illustrated in FIG. 2 may include an additional layerof undoped AlGaN about 6-9 Å thick between the active regions 125 andthe layer 22.

An AlGaN layer 30 doped with a p-type impurity such as magnesium isprovided on layer 22. The AlGaN layer 30 may be between about 0 and 300Å thick inclusive and is preferably about 130 Å thick. A contact layer32 of p-type GaN is provided on the layer 30 and is preferably about1800 Å thick. Ohmic contacts 24 and 25 are provided on the p-GaN contactlayer 32 and the substrate 10, respectively. Ohmic contacts 24 and 25are provided on the p-GaN contact layer 32 and the substrate 10,respectively.

FIG. 4 illustrates further embodiments of the present inventionincorporating a Group III-nitride layer incorporating Indium on theactive region of the device, For example, an InAlGaN cap structure maybe provided. The embodiments of the present invention illustrated inFIG. 4 include a layered semiconductor structure 400 comprising galliumnitride-based semiconductor layers grown on a substrate 10. As describedabove, the substrate 10 may be SiC, sapphire or bulk gallium nitride. Inparticular embodiments of the present invention, the substrate 10 is aSiC substrate having a thickness of from about 50 to about 800 μm and insome embodiments, about 100 μm.

As is illustrated in FIG. 4, LEDs according to particular embodiments ofthe present invention may include a conductive buffer layer 11, a firstsilicon-doped GaN layer 12, a second silicon doped GaN layer 14, asuperlattice structure 16 comprising alternating layers of silicon-dopedGaN and/or InGaN, an active region 325 comprising a multi-quantum wellstructure, an undoped AlInGaN layer 40, an AlGaN layer 30 doped with ap-type impurity, and a GaN contact layer 32, also doped with a p-typeimpurity. The LEDs may further include an n-type ohmic contact 23 on thesubstrate 10 and a p-type ohmic contact 24 on the contact layer 32. Inembodiments of the present invention where the substrate 10 is sapphire,the n-type ohmic contact 23 would be provided on n-type GaN layer 12and/or n-type GaN layer 14.

As described above with reference to FIGS. 1 and 2, the buffer layer 11may be n-type AlGaN. For example, the buffer layer 11 may be AlGaN dopedwith Si and having a thickness of from about 100 to about 10,000 Å. Incertain embodiments the thickness is about 1500 Å. The GaN layer 12 maybe doped with Si and may have a thickness of from about 5000 to 50,000 Åthick inclusive and, in particular embodiments, is about 18,000 Å thick.The GaN layer 12 may be doped with silicon at a level of about 5×10¹⁷ to5×10¹⁸ cm⁻³, The superlattice structure 16 may also be provided asdescribed above with reference to FIG. 1. For example, the superlatticestructure 16 may have from 3 to 35 periods of InGaN/GaN. The thicknessof the periods may be from about 30 to about 100 Å. In particularembodiments of the present invention, twenty five (25) periods ofInGaN/GaN are provided with the thickness of a period of layers beingabout 70 Å and the thickness of the GaN or InGaN layer being about 15 Åwith the other layer making up the remainder.

The active region 325 may include a multi-quantum well structure thatincludes multiple InGaN quantum well layers 320 separated by barrierlayers 318. The barrier layers 318 comprise In_(X)Ga_(1-X)N where 0≦X<1.Preferably the indium composition of the barrier layers 318 is less thanthat of the quantum well layers 320, so that the barrier layers 318 havea higher bandgap than quantum well layers 320. The barrier layers 318and quantum well layers 320 may be undoped (i.e. not intentionally dopedwith an impurity atom such as silicon or magnesium). However, it may bedesirable to dope the barrier layers 318 with Si at a level of less than5×10¹⁹ cm⁻³, particularly if ultraviolet emission is desired.

In further embodiments of the present invention, the barrier layers 318comprise Al_(X)In_(Y)Ga_(1-X-Y)N where 0<X<1, 0≦Y<1 and X+Y≦1. Byincluding aluminum in the crystal of the barrier layers 318, the barrierlayers 318 may be lattice-matched to the quantum well layers 320,thereby allowing improved crystalline quality in the quantum well layers320, which can increase the luminescent efficiency of the device.

The active region 325 may also be provided as illustrated in FIG. 3 anddescribed above with reference to FIGS. 1 through 3. In particularembodiments of the present invention, the active region 325 includes 3or more quantum wells and in certain embodiments, eight (8) quantumwells are provided. The thickness of the quantum well structures may befrom about 30 to about 250 Å. In particular embodiments of the presentinvention, the thickness of a quantum well structure may be about 120 Åwith the thickness of the well layer being about 25 Å.

The LED structure illustrated in FIG. 4 may also include a spacer layerdisposed between the superlattice 16 and the active region 325 asdescribed above.

Returning to FIG. 4, a Group III-nitride capping layer 40 that includesIndium may be provided on the active region 325 and, more specifically,on the quantum well 320 of the active region 325. The Group III-nitridecapping layer 40 may include InAlGaN between about 10 and 320 Å thickinclusive. The capping layer 40 may be of uniform composition, multiplelayers of different compositions and/or graded composition. Inparticular embodiments of the present invention, the capping layer 40includes a first capping layer having a composition ofIn_(x)Al_(y)Ga_(1-x-y)N, where 0<x≦0.2 and 0≦y≦0.4 and has a thicknessof from about 10 to about 200 Å and a second capping layer having acomposition of In_(w)Al_(z)Ga_(1-w-z)N, where 0<w≦0.2 and y≦z<1 and hasa thickness of from about 10 to about 120 Å. In certain embodiments ofthe present invention, the first capping layer has a thickness of about80 Å, x=0.1 and y=0.25 and the second capping layer has a thickness ofabout 30 Å, w=0.05 and z=0.55. The capping layer 40 may be grown at ahigher temperature than the growth temperatures in the active region 325in order to improve the crystal quality of the layer 40. Additionallayers of undoped GaN or AlGaN may be included in the vicinity of layer40. For example, a thin layer of GaN may be provided between a lastquantum well layer and the capping layer 40. The capping layer 40 thatincludes indium may be more closely lattice matched to the quantum wellsof the active region 325 and may provide a transition from the latticestructure of the active region 325 to the lattice structure of thep-type layers. Such a structure may result in increased brightness ofthe device.

An AlGaN hole injection layer 42 doped with a p-type impurity such asmagnesium is provided on the capping layer 40. The AlGaN layer 42 may bebetween about 50 and 2500 Å thick inclusive and, in particularembodiments, is about 150 Å thick. The AlGaN layer 42 may be of thecomposition of Al_(x)Ga_(1-x)N, where 0≦x≦0.4. In particular embodimentsof the present invention, x=0.23 for the AlGaN layer 42. The AlGaN layer42 may be doped with Mg. In some embodiments of the present invention,the layer 42 may also include Indium.

A contact layer 32 of p-type GaN is provided on the layer 42 and may befrom about 250 to abut 10,000 Å thick and in some embodiments, about1500 Å thick. In some embodiments, the contact layer 32 may also includeIndium. Ohmic contacts 24 and 25 are provided on the p-GaN contact layer32 and the substrate 10, respectively. Ohmic contacts 24 and 25 areprovided on the p-GaN contact layer 32 and the substrate 10,respectively.

In some embodiments of the present invention, the indium containingcapping layer 40 may be provided in light emitting devices as described,for example, in U.S. Provisional Patent Application Ser. No. 60/591,353entitled “ULTRA-THIN OHMIC CONTACTS FOR P-TYPE NITRIDE LIGHT EMITTINGDEVICES” and filed concurrently herewith, U.S. patent application Ser.No. 10/899,793 entitled “LIGHT EMITTING DEVICES HAVING A REFLECTIVE BONDPAD AND METHODS OF FABRICATING LIGHT EMITTING DEVICES HAVING REFLECTIVEBOND PADS” and filed concurrently herewith, U.S. Pat. No. 6,664,560,U.S. patent application Ser. No. 10/881,814 entitled “LIGHT EMITTINGDEVICES HAVING CURRENT BLOCKING STRUCTURES AND METHODS OF FABRICATINGLIGHT EMITTING DEVICES HAVING CURRENT BLOCKING STRUCTURES,” filed Jun.30, 2004, U.S. Patent Publication No. 2003/0123164 entitled “LIGHTEMITTING DIODES INCLUDING SUBSTRATE MODIFICATIONS FOR LIGHT EXTRACTIONAND MANUFACTURING METHODS THEREFOR” and/or in U.S. Patent PublicationNo. 2003/0168663 entitled “REFLECTIVE OHMIC CONTACTS FOR SILICON CARBIDEINCLUDING A LAYER CONSISTING ESSENTIALLY OF NICKEL, METHODS OFFABRICATING SAME, AND LIGHT EMITTING DEVICES INCLUDING THE SAME,” thedisclosures of which is incorporated herein as if set forth in itsentirety.

Electroluminescence (EL) testing was performed on LED wafers havingdevices with and without the indium containing capping layer, inparticular, an InAlGaN capping layer, as illustrated in FIG. 4. The ELtest is an on-wafer test that measures the brightness of LED epitaxialstructures. This test is not influenced by the LED fabrication method,chip shaping, or packaging method. Approximately 176 wafers with thestructure including the indium containing layer and 615 wafers withoutthe indium containing layer were tested. Both structures were growncontinuously on a number of reactors. The reactors were all essentiallythe same (i.e. none have any special modification for increasedbrightness, all have been and continue to be suitable for productionuse). The data from the wafers was binned and shows that the structurewith the indium containing layer was approximately 1.15 to 1.25 timesbrighter than the structure without the indium containing layer.

While embodiments of the present invention have been described withmultiple quantum wells, the benefits from the teachings of the presentinvention may also be achieved in single quantum well structures. Thus,for example, a light emitting diode may be provided with a singleoccurrence of the structure 221 of FIG. 3 as the active region of thedevice. Thus, while different numbers of quantum wells may be utilizedaccording to embodiments of the present invention, the number of quantumwells will typically range from 1 to 10 quantum wells.

While embodiments of the present invention have been described withreference to gallium nitride based devices, the teachings and benefitsof the present invention may also be provided in other Group IIInitrides. Thus, embodiments of the present invention provide Group IIInitride based superlattice structures, quantum well structures and/orGroup III nitride based light emitting diodes having superlatticesand/or quantum wells.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

What is claimed is:
 1. A light emitting diode, comprising: an n-typeGroup III nitride layer; a Group III nitride light emitting diode activeregion on the n-type Group III nitride layer, the light emitting diodeactive region comprising at least one quantum well structure; and anundoped Group III nitride capping layer comprising indium on the lightemitting diode active region opposite from the n-type Group III nitridelayer, wherein the capping layer is distinct from the light emittingdiode active region, and wherein the capping layer is directly on abinary Group III nitride layer.
 2. The light emitting diode of claim 1,wherein the capping layer comprising indium comprises a quaternarylayer.
 3. The light emitting diode of claim 1, wherein the binary GroupIII nitride layer comprises a barrier layer of the active region.
 4. Thelight emitting diode of claim 1, wherein the binary Group III nitridelayer is between the active region and the undoped capping layer.
 5. Thelight emitting diode of claim 1, wherein the undoped Group III nitridecapping layer further comprises aluminum.
 6. The light emitting diode ofclaim 1, further comprising: a p-type Group III nitride layer directlyon the undoped Group III nitride capping layer and remote from theactive region.
 7. The light emitting diode of claim 1, wherein theundoped Group III nitride capping layer provides a transition from alattice structure of the light emitting diode active region to a latticestructure of a p-type layer thereon.
 8. The light emitting diode ofclaim 1, wherein the undoped Group III nitride capping layer does notprovide photon emission due to carrier recombination therein.
 9. A lightemitting diode, comprising: an n-type Group III nitride layer; a GroupIII nitride light emitting diode active region on the n-type Group IIInitride layer, the light emitting diode active region comprising atleast one quantum well structure; and an undoped Group III nitridecapping layer comprising indium on the light emitting diode activeregion opposite from the n-type Group III nitride layer, wherein thecapping layer is distinct from the light emitting diode active region,and wherein the capping layer is directly on a quaternary barrier layerof the active region.